A conventional pressure sensor is disclosed in U.S. Pat. No. 4,500,864. In one embodiment therein, a strain gauge of amorphous metal material is formed directly on the diaphragm by, for example, sputtering. The diaphragm is of an insulating type material such as ceramic or glass materials. However, due to the materials utilized for the diaphragm, for example glass materials, the electrical output of the sensor versus the pressure exerted upon the sensor experiences a hysteresis effect. Additionally at a constant pressure exerted upon the sensor, the electrical output with respect to time-elapse of the sensor is not consistent due to the elasticity of the glass material utilized for the diaphragm.
Also disclosed in U.S. Pat. No. 4,500,864 is an alternative embodiment wherein the diaphragm is of an electrically conductive material and an insulating layer is formed onto the diaphragm and onto the insulating layer is subsequently formed the strain gauge by, for example, physical vapor deposition. As is readily apparent, the insulating material is interposed between the strain gauge and the diaphragm so as to insure the insulation therebetween. Though the thickness of the insulating material is not detailed in the specification of U.S. Pat. No. 4,500,864, a commercial embodiment thereof has insulating material having a thickness of 10 to 15 microns. However, at such thicknesses of the insulating material, the insulating material is subject to separation from the diaphragm upon excessive deformation of the diaphragm.
Thus there exist the need for such a sensor which does not suffer from hysteresis or elasticity effects due to the diaphragm composition and which does not suffer from insulating material separation from the diaphragm upon excessive deformation of the diaphragm.